Method for controlling data transmission in a wireless V.24 data transmission system operating between a data terminal and a data transmission device for data telecommunication

ABSTRACT

In a wireless V.24 data transmission system operating between a data terminal and a data transmission device for data telecommunication having a first data transmission apparatus connected to the data terminal by means of a V.24 cable and a second data transmission apparatus connected to the data terminal by means of a V.24 cable, the apparatus may in turn be connected for wireless communication by means of an air interface. In order to control data transmission in such a way that baud rate changes can be easily detected, the baud rate is detected by the first data transmission apparatus while the autobauding function is activated in the first data transmission apparatus and in the data transmission device. The baud rate is transmitted by signaling to the second data transmission apparatus and is regulated therein parallel to the command data (AT commands) to be sent.

BACKGROUND OF THE INVENTION

Data telecommunication (datel) is the mutual sending and receiving ofdata or data signals (packet data) between a data terminal equipmentitem—e.g. personal computer, data terminals, DP systems etc.—and aremote data terminal equipment unit—e.g. personal computer, dataterminals, DP systems etc.—via a telecommunication network, for examplea public telecommunication network (ISDN, PSTN etc.). So that the dataor data signals sent by the data terminal equipment unit can betransmitted via the telecommunication network, a network facility, theso-called data communication equipment unit, is provided between thedata terminal equipment unit and the telecommunication network. Apartfrom the PC card (previously: PCMCIA card), the most widely used datacommunication equipment item is the modem (made up ofmodulator/demodulator) [compare also the utility model DE 297 14 588U1].

The modem is an electrical data communication equipment unit operatingon the basis of the carrier-current method for use on analogtransmission paths of limited bandwidth—e.g. telecommunication lines(e.g. a/b circuit pair, ISDN-S_(O)-BUS etc.) of the telecommunicationnetwork which converts digital data signals into analog data signals andconversely and transmits them. Furthermore, a multiplicity of methods ofthe V series standardized by the International Telecommunication Union -Telecommunication Standards (ITU-T) - are implemented in modems.

FIG. 1 shows a data telecommunication scenario based on a V.24 datatransmission system. A V.24 data transmission system is connected to aremote V.24 data transmission system via a public telecommunicationnetwork, for example a PSTN (Public Switched Telecommunication Network)exhibiting an a/b circuit pair or an ISDN (Integrated Services DigitalNetwork) exhibiting an ISDN-S₀-bus. The V.24 data transmission systemexhibits a data terminal equipment unit DTE constructed, for example, aspersonal computer and a data communication equipment unit DCEconstructed, for example, as a modem, which are connected to one anothervia a V.24 cable (V.24 interface) K_(V.24).

Analogously to the above, the remote V.24 data transmission systemexhibits a remote data terminal equipment unit DTE_(r) constructed, forexample, as a personal computer and a remote data communicationequipment unit DCE_(r) constructed, for example, as a modem which arealso connected to one another via a V.24 cable (V.24 interface)K_(V.24).

The data terminal equipment unit DTE, DTE_(r) contains a systemcontroller SST with a user interface BOF, application software ASW and adriver TR as an interface adapter between software (applicationsoftware) and hardware (data communication equipment unit or,respectively, modem).

The driver TR is specific to the modem manufacturer and preferablyconstructed as CAPI (Common ISDN Application Programmable Interface;standardized communication interface for user software for theerror-tolerant ISDN telecommunication with the personal computer) driveror as TAPI (Telephone Application Programmable Interface) driver.

A plurality of the data communication equipment units DCE which can beobtained on the market, e.g. analog modems and ISDN terminal adaptersexternal to the PC are controlled via a HAYES instruction set (or HAYESstandard). The HAYES standard was originally an American industrystandard for modem communication, especially for modem control by thedata terminal equipment unit DTE. It is also called the AT standardbecause almost all instructions of the HAYES instruction set begin withthe prefix “AT” (Attention) comprising the ASCII characters A and T. Thestandard which, in the meantime, has been introduced throughout theworld, is the subject matter of an ITU Recommendation (InternationalTelecommunication Union) designated by “ITU-T V.25ter”. Instead of theprefix “AT”, the prefix “at”, the prefix “A/” or the prefix a/” can alsobe used.

In these modems, the modem driver TR of the data terminal equipment unitDTE changes the baud rate at the V.24 interface depending on the datatransmission phase (e.g. connection set-up, negotiation of thetransmission parameters etc.). This change in baud rate is transmittedvia the V.24 cable K_(V.24) to the data communication equipment unit ormodem, respectively, DCE, but not by means of signaling. Thus, the modemDCE must automatically detect the newly set baud rate and adapt itselfto the driver TR (autobauding). The relevant rule is: the baud rate atwhich the “AT” character sequence is transmitted is valid until the next“AT” character sequence is received.

This autobauding is active in the modems until the modem has changedinto the user data transmission mode, or the so-called “transparentmode” after a connection set-up. In this mode, a “point-to-point”connection (“end-to-end” connection) exists with the remote datacommunication equipment unit or, respectively, remote modem DCE_(r.)Autobauding is then switched off so that “AT” character sequences arenot interpreted in the user data stream and there is possibly anunwanted change in baud rate at the modem.

The V.24 cable or, respectively, V.24 interface K_(V.24) supports themodem operation on a personal computer by means of various lines (statuslines) in accordance with ITU-T Specification V.24 , March 1993, pages 1to 19. These lines are:

1. A transmit data line TxD for data transmission,

2. a receive data line RxD for data transmission,

3. an RTS (Ready To Send) line RTS for the “hardware handshake” type oftransmission for transmitting the “READY TO SEND” state (“RTS” state),

4. a CTS (Clear To Send) line CTS for the “hardware handshake” type oftransmission for transmitting the “CLEAR TO SEND” state (“ICTS” state),

5. an RI (Ring Indication) line RI for detecting ringing at the modem,

6. a DSR (Data Set Ready) line DSR on which the modem reports to thepersonal computer that it is switched on,

7. a DTR (Data Terminal Ready) line DTR on which the personal computerreports to the modem that it is switched on and is ready to acceptcalls,

8. a DCD (Data Channel Detection) line DCD on which the modem reports tothe personal computer that it has accepted and set up the connection toa remote modem,

9. a ground (GrouND) line GND.

If the V.24 cable or V.24 interface K_(V.24) does not have the ninelines listed above but has fewer than nine, e.g. seven, this 7-wirecable can still support the modem operation on the personal computer.This is possible due to the fact that, instead of the “hardwarehandshake” on the RTS/CTS lines, a “software handshake” type oftransmission is performed for transmitting the “RTS”, “CTS” states—e.g.by means of an XON/XOFF protocol - on the transmit/receive data linesTxD, RxD. In the “software handshake”, the data stream transmittedbetween the data terminal equipment unit DTE and the data communicationequipment unit DCE is analyzed in the data terminal equipment unit DTEand the data communication equipment unit DCE, all “software handshakesignals” are interpreted and measures are correspondingly initiated.

For an application scenario in which the data terminal equipment unitDTE and the data communication equipment unit DCE are spatiallyseparated from one another, e.g. by several meters, the cord-connectedV.24 data transmission system shown in FIG. 1 exhibits the disadvantagethat first, a V.24 cable K_(V.24), the length of which corresponds tothe spatial arrangement of data terminal equipment unit DTE and datacommunication equipment unit DCE, is required for the datatelecommunication and, secondly, a large, not inconsiderable effort isexpended for running the cable for the installation of the system withsuch cable lengths.

Analogously to cordless telephony, it is therefore desirable and alsoimaginable to replace the cord-connected V.24 data transmission systemaccording to FIG. 1 with a cordless V.24 data transmission system.

On the basis of FIG. 1, FIG. 2 shows such a cordless V.24 datatransmission system for data telecommunication. The remote V.24 datatransmission system, not completely shown in FIG. 2, can either becord-connected according to FIG. 1 or cordless like the cordless V.24data transmission system in FIG. 2. Compared with the cord-connectedV.24 data transmission system in FIG. 1, the V.24 cable or V.24interface K_(V.24) between the data terminal equipment unit DTE and thedata communication equipment unit DCE are split apart compared with thecord-connected V.24 data transmission system in FIG. 1 and are connectedat the two ends of the cable caused by the splitting to in each case onedata transmission device.

The two data transmission devices, a first data transmission device DTD1connected to the data terminal equipment unitm DTE by the V.24 cable orV.24 interface K_(V.24) and a second data transmission device DTD2connected to the data communication equipment unit DCE by the V.24 cableor V.24 interface K_(V.24) are connected to one another by an airinterface LSS for wireless telecommunication.

Air interfaces are wireless telecommunication interfaces in whichmessages are transmitted via a remote transmission link between amessage source (e.g. first data transmission device DTD1) and a messagesink (e.g. second data transmission device DTD2) wirelessly on the basisof various message transmission methods FDMA (Frequency DivisionMultiple Access), TDMA (Time Division Multiple Access) and/or CDMA (CodeDivision Multiple Access)—e.g. in accordance with radio standards suchas DECT [Digital Enhanced (previously: European) CordlessTelecommunication; compare Nachrichtentechnik Elektronik 42 (1992)Jan./Feb. No. 1, Berlin, DE; U. Pilger “Struktur des DECT-Standards”[Structure of the DECT standard], pages 23 to 29 in conjunction withETSI publication ETS 300175-1 . . . 9, October 1992 and DECT publicationof the DECT Forum, February 1997, pages 1 to 16], GSM [Groupe SpécialeMobile or Global System for Mobile Communication; compare InformatikSpektrum 14 (1991) June, No. 3, Berlin, DE; A. Mann: “Der GSM-Standard -Grundlage fur digitale europäische Mobilfunknetze” [The GSM standard -basis for digital European mobile radio networks], pages 137 to 152 inconjunction with the publication telekom praxis 4/1993, P. Smolka“GSM-Funkschnittstelle - Elemente und Funktionen” [The GSM radiointerface - elements and functions], pages 17 to 24], UMTS (compareFunkschau 6/98: R. Sietmann “Ringen um die UMTS-Schnittstelle” [Fightingfor the UMTS interface], pages 76 to 81) WACS or PACS, IS-54, IS-95,PHS, PDC etc. (compare IEEE Communications Magazine, January 1995, pages50 to 57; D. D. Falconer et al.: “Time Division Multiple Access Methodsfor Wireless Personal Communications”).

The air interface LSS provided in FIG. 2 is preferably the DECT airinterface. According to the publication “Vortrag von A. Elberse, M.Barry, G. Fleming zum Thema: [lecture by A. Elberse, M. Barry, G.Fleming on the subject]: DECT Data Services - DECT in fixed and mobilenetworks”, 17/18 June 1996, Sofitel Hotel, Paris; pages 1 to 12 ; andsummary”, on the basis of the printed document “NachrichtentechnikElektronik 42 (1992) Jan./Feb. No. 1, Berlin, DE; U. Pilger “Strukturdes DECT-Standards”, (Structure of the DECT standard), pages 23 to 29;in conjunction with ETSI publication ETS 300175-1 . . . 9, October 1992and the printed documents Components 31 (1993), Vol. 6, pages 215 to218; S. Althammer, D. Bruackmann: “Hochoptimierte IC's fürDECT-Schnurlostelefone” [Highly optimized ICs for cordless DECTtelephones] and WO 96/38991 (compare FIGS. 5 and 6 with the respectivelyassociated description) - the DECT technology is suitable for the basicapplicability of the DECT tecyhnology (Digital Enhanced CordlessTelecommunication) for the wireless mobile remote transmission of voiceand/or packet data in which the user can both become his own networkoperator and also has an access capability to a high-leveltelecommunication network due to the DECT network access technology withrespect to the remote transmission of user data.

If it is intended to replace a V.24 cable link, e.g. between a personalcomputer and a modem, by means of a cordless data transmission linkaccording to FIGS. 1 and 2, it is also necessary to offer the feature of“autobauding” (automatic baud rate detection at the V.24 interface)normally used in modems at the cordless data transmission link so thatthe modem drivers supplied with a modem can still be used and a changein baud rate can thus be detected.

SUMMARY OF THE INVENTION

An object of the invention is to control the data transmission in acordless V.24 data transmission system operated between a data terminalequipment unit and a data communication equipment unit meant for thepurpose of data telecommunication, in such a manner that a change inbaud rate can be detected in a simple manner.

According to the method of the present invention for controlling datatransmission in a cordless V.24 data transmission system operatedbetween a data terminal equipment unit in a data communication equipmentunit for data telecommunication, the V.24 data transmission system has afirst V.24 data transmission device and a second V.24 data transmissiondevice connected to one another via an air interface. The first V.24data transmission device is connected to the data terminal equipmentunit. The second V.24 data transmission device is connected to the datacommunication equipment unit and the data communication equipment unitis connected to a remote data communication equipment unit with adownstream remote data terminal equipment unit. When the data terminalequipment unit, the data communication equipment unit, and the V.24 datatransmission devices are switched on, the V.24 data transmissiondevices, the data terminal equipment unit, and the data communicationequipment unit are operated in an instruction data transmission mode. Inthe instruction data transmission mode, the data terminal equipment unittransmits instruction data at different baud rates depending on datatransmission phase. When an autobauding function is activated, the firstV.24 data transmission device detects that instruction data have beentransmitted at different baud rates or that a change in buad rate hastaken place. The respective buad rate is transmitted to the second V.24data transmission device by means of signaling, and the instruction datasent by the data terminal equipment unit with the different buad ratesis transmitted to the second V.24 data transmission device. The secondV.24 data transmission device sets the baud rates received from thefirst V.24 data transmission device in parallel with the receivedinstruction data and transmits the instruction data thus set to the datacommunication equipment unit. When the autobauding function isactivated, the data communication equipment unit detects that theinstruction data have been transmitted at different buad rates or that achange in baud rate has taken place.

An idea of the invention is that in a cordless V.24 data transmissionsystem operated between a data terminal equipment unit (e.g. a personalcomputer) and a data communication equipment unit (e.g. a modem) for thepurpose of data telecommunication, with a first data transmission deviceconnected to the data terminal equipment unit via a V.24 cable and witha second data transmission device connected to the data communicationequipment unit via a V.24 cable, which, in turn, can be connected via anair interface by wireless telecommunication, a change in baud rate isdetected in that, when the autobauding function is activated in a firstdata transmission device and in the data communication equipment unit,the baud rate in each case detected by the first data transmissiondevice is transmitted to the second data transmission device by means ofsignalling and is there set in parallel with instruction data (ATinstructions) to be sent out.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a data telecommunication system based ona V.24 data transmission system according to the prior art;

FIG. 2 shows a block diagram of a cordless V.24 data transmission systemfor data telecommunication according to the prior art; and

FIG. 3 shows a cordless V.24 data transmission system in block diagramformat according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the preferred embodimentillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended, such alterations andfurther modifications in the illustrated device, and such furtherapplications of the principles of the invention as illustrated thereinbeing contemplated as would normally occur to one skilled in the art otwhich the invention relates.

A first exemplary embodiment of the invention will be explained withreference to FIG. 3.

FIG. 3 shows the cordless V.24 data transmission system according toFIG. 2 in which the data transmission is controlled as follows:

When the data terminal equipment unit DTE, the data communicationequipment unit DCE and the V.24 data transmission devices DTD1, DTD2 areswitched on, the V.24 data transmission devices DTD1, DTD2, the dataterminal equipment unit DTE and the data communication equipment unitDCE are operated in an instruction data transmission mode.

In the instruction data transmission mode, the data terminal equipmentunit DTE transmits instruction data KD at different baud rates BRdepending on the data tranmission phase.

When the autobauding function is activated, the first V.24 datatransmission device DTD1 detects that the instruction data KD have beentransmitted at different baud rates BR or, respectively, that a changein baud rate has taken place, transmits the respective baud rate BR tothe second V.24 data transmission device DTD2 by means of signalling SIGand transmits the instruction data KD sent by the data terminalequipment item with the different baud rates BR to the second V.24 datatransmission device DTD2.

The second V.24 data transmission device DTD2 sets the baud rates BRreceived from the first V.24 data transmission device DTD1 in parallelwith the received instruction data KD and transmits the instruction dataKD thus set to the data communication equipment unit DCE.

When the autobauding function is activated, the data communicationequipment item DCE detects that the instruction data KD have beentransmitted at different baud rates BR or, respectively, that a changein baud rate has taken place.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spriti of the inventionare desired to be protected.

We claim:
 1. A method for controlling data transmission in a cordlessV.24 data transmission system operated between a data terminal equipmentunit and a data communication equipment unit for data telecommunication,the V.24 data transmission system having a first V.24 data transmissiondevice and a second V.24 data transmission device connected to oneanother via an air interface, the first V.24 data transmission devicebeing connected to the data terminal equipment unit, the second V.24data transmission device being connected to the data communicationequipment unit, and the data communication equipment unit beingconnected to a remote data communication equipment unit with adownstream remote data terminal equipment unit, comprising the steps of:when the terminal equipment unit, the data communication equipment unitand the V.24 data transmission devices are switched on, operating theV.24 data transmission devices, the data terminal equipment unit and thedata communication equipment unit in an instruction data transmissionmode; in the instruction data transmission mode, with the data terminalequipment unit, transmitting instruction data at different baud ratesdepending on data transmission phase; when an autobauding function isactivated, with the first V.24 data transmission device detecting thatinstruction data have been transmitted at different baud rates or that achange in baud rate has taken place, transmitting the respective baudrate to the second V.24 data transmission device by means of signaling,and transmitting the instruction data sent by the data terminalequipment unit with the different baud rates to the second V.24 datatransmission device; with the second V.24 data transmission device,setting the baud rates received from the first V.24 data transmissiondevice in parallel with the received instruction data and transmittingthe instruction data thus set to the data communication equipment unit;and when the autobauding function is activated, with the datacommunication equipment unit detecting that the instruction data havebeen transmitted at different baud rates or that a change in baud ratehas taken place.
 2. The method of claim 1 wherein the instruction dataare Hayes-related instructions with a Hayes prefix “AT” Attention. 3.The method of claim 1 wherein a modem is used as the data communicationequipment unit and a personal computer is used as the data terminalequipment unit.
 4. The method of claim 1 wherein a DECT air interface isused as the air interface.
 5. A method for controlling data transmissionin a cordless data transmission system operated between a data terminalequipment unit and a data communication equipment unit for datatelecommunication, the data transmission system having a first datatransmission device and a second data transmission device connected toone another via an air interface, the first data transmission devicebeing connected to the data terminal equipment unit, the second V.24data transmission device being connected to the data communicationequipment unit, and the data communication equipment unit beingconnected to a remote data communication equipment unit with adownstream remote data terminal equipment unit, comprising the steps of:when the terminal equipment unit, the data communication equipment unitand the data transmission devices are switched on, operating the datatransmission devices, the data terminal equipment unit and the datacommunication equipment unit in an instruction data transmission mode;in the instruction data transmission mode, with the data terminalequipment unit, transmitting instruction data at different baud ratesdepending on data transmission phase; when an autobauding function isactivated, with the first data transmission device detecting thatinstruction data have been transmitted at different baud rates or that achange in baud rate has taken place, transmitting the respective baudrate to the second data transmission device by means of signaling, andtransmitting the instruction data sent by the data terminal equipmentunit with the different baud rates to the second data transmissiondevice; with the second data transmission device, setting the baud ratesreceived from the first data transmission device in parallel with thereceived instruction data and transmitting the instruction data thus setto the data communication equipment unit; and when the autobaudingfunction is activated, with the data communication equipment unitdetecting that the instruction data have been transmitted at differentbaud rates or that a change in baud rate has taken place.